Use of body implants in reconstructive surgery following mastectomy has been practiced for some time with a high rate of patient satisfaction. Early implants were made of a spongy material such as polyurethane which left much to be desired. Present day implants are generally made from a polysilicone elastomer sac filled with a silicone gel or mixture of silicone gel and silicone fluid. The first successful implant of such a prosthesis is credited to T. D. Cronin (Cronin, U.S. Pat. No. 3,293,663). Cronin's implant comprised a flexible sac made from silicone rubber with a silicone gel fill as described in U.S. Pat. No. 3,020,260. A polyester fabric was attached to the back of the sac which was invaded by tissue thus attaching the prosthesis to the chest wall.
Colette et al. U.S. Pat. No. 3,665,520 describes a similar prosthesis with an elongated tab extending toward the axilla region. A polyester felt is placed only along the edge of the tab for attachment to the chest wall. This sac was made of an organopolysiloxane polycarbonate block copolymer and filled with a silicone gel.
Lynch U.S. Pat. No. 3,883,902 describes a unitary sterile assembly including an empty silicone rubber sac attached to a reservoir for filling the sac with silicone gel after implantation.
Brill U.S. Pat. No. 4,100,627 recognized the problem of silicone gel migration in previous silicone gel-filled prosthetic devices. Brill used a conventional polydimethylsiloxane sac but substituted a cross-linked polydimethylsiloxane gel which is said to reduce leakage. However, since cross-linking is not 100% efficient, some un-crosslinked oil remains which will continue to leak. The polydimethylsiloxane elastomer used to make the sac can also contain other siloxane units such as methylvinylsiloxane, methylphenylsiloxane, diphenylsiloxane and 3,3,3-trifluoropropylsiloxane and can be end-blocked with conventional units such as dimethylvinylsiloxy, trimethylsiloxy or methylphenylvinylsiloxy units. The silicone rubber contains fillers such as silica, processing aids, additives, pigments and can be vulcanized or cured with organic peroxides or by irradiation.
Frisch U.S. Pat. No. 4,205,401 describes a mammary implant constructed to resist the effects of fibrous capsular contracture which tends to distort an implant into a spherical shape surrounded by a stiff fibrous capsule. Frisch lists various materials said to be useful in making the sac. These are cellulose acetate, cellulose acetate butyrate, cellulose nitrate, crosslinked polyvinyl alcohol, polyurethanes, nylon 6, nylon 66, aromatic nylon, polyvinyl acetate, plasticized polyvinyl acetate, polyvinyl butyrate, ethylene vinyl acetate copolymer, polyethylene, polypropylene, polyisobutylene, polyvinylchloride, plasticized polyvinylchloride, natural rubber, and synthetic elastomers such as silicone rubber and polybutadiene. Except for silicone rubber the list appears to be highly speculative. Frisch also discusses the technique of making the implant sac by dip coating a shaped mandrel, curing the sac on the mandrel and removing the sac from the mandrel.
Redinger et al. U.S. Pat. No. 4,455,691 notes the belief on the part of many surgeons that the reduction of silicone gel and oil migration from implants would be a definite improvement in reducing the problem of fibrous contraction which is said to occur in up to 40% of patients after implant (Baker et al. "Bleeding of Silicone From Bag-Gel Breast Implants and Its Clinical Relation to Fibrous Capsule Reaction", Plastic and Reconstructive Surgery, June 1976, Vol. 61, No. 6; Hausner et al. "Foreign-Body Reaction to Silicone Gel in Axillary Lymph Nodes After an Augmentation Mammaplasty", Plastic and Reconstructive Surgery, Sept. 1978, Vol. 62, No. 3). Redinger et al. impedes the migration of gel and oil through the sac walls by using a sac wall made of the reaction product of polydimethylsiloxane and either 3,3,3-trifluoropropylpolysiloxane, diphenylpolysiloxane or methylphenylpolysiloxane. Multi-layer sacs are disclosed wherein one of the layers is the barrier film. Methods for making these multi-layer implant sacs are discussed in detail.